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Chalcogenide glass (ChG) which contain one or more chalcogen elements is one of the most interesting material for infrared (IR) photonics owing to its unique optical properties, such as high refractive index, strong optical nonlinearity, and wide infrared transparency.
In this paper, we experimentally demonstrate high-quality ChG micro-disk resonators on oxidized silicon wafers fabricated by the standard UV photolithography and lift-off. Quality factor of micro-disk resonators are often limited by optical scattering loss induced by lithographically defined edge roughness. Thermal reflow of chalcogenide itself may significantly reduce edge roughness, but thermal shrinkage and deformation of the material during the reflow make it hard to precisely control the overall size and shape of the fabricated device. Instead, we reduce the sidewall roughness using thermal reflow of photoresist and modified bi-layer lift-off process. Typically, the thermal reflow of resist destroys the undercut or vertical sidewall profile of developed resist layer, making it extremely difficult or impossible to subsequently use lift-off or etching for patterning. We address this issue by first wet etching the silica substrate to undercut the reflowed photoresist, creating an overhang required for lift-off. ChG film is then deposited to produce a micro-disk resonator with much improved edge roughness. To finally create a micro-disk resonator on a silica pillar, we adopt vapor etching of the silica substrate. With optimized conditions of reflow and undercut, we obtained high quality ChG disk-resonators with extremely smooth edge profile, operating in the infrared region. Complete characterization results will be presented at the conference. The new method is compatible with traditional CMOS process and thus expected to have great potentials for fabricating high quality photonic integrated devices.
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